Many researches have been made in respect to high-temperature superconducting materials which can function at the temperature of liquid nitrogen of 77 K., and there have been provided reports on the characteristics of the resulting superconducting films. It is well known that a high-quality oxide superconducting film can be obtained when the oxide superconducting thin film of YBa.sub.2 Cu.sub.3 O.sub.7-x and the like is formed on the singlecrystalline substrate of SrTiO.sub.3 and the like.
On the contrary, it is known that the oxide superconducting film which has relatively low current-transport properties of critical current density(Jc) of 10.sup.3 to 10.sup.4 A/cm.sup.2 tends to be obtained due to the difference of the orientation when the oxide superconducting film is directly formed on the polycrystalline substrate of silver, Ni-based alloy, YSZ(Yttrium Stabilized Zirconia), Al.sub.2 O.sub.3 and the like.
Therefore, it has been tried to deposit an intermediate buffer layer for preventing mutual diffusion between an oxide superconductor and a substrate, particularly a metallic substrate so as to get high current-transport properties. Ag, YSZ, MgO, YSZ-Pt, YSZ-Ag, BaTiO.sub.3, TiN and the like are used as this intermediate buffer layer. On the other hand, there are used coating method, laser ablation (LPVD) method, CVD method, ion-beam sputtering method and the like as the conventional technique for depositing a thin film on a substrate.
On pages 2594 to 2596 of "Applied Physics Letters, vol. 57, No. 24 (Dec. 10, 1990)", it is reported that Ashok Kumar et al. for North Carolina state university grow YSZ at the film deposition temperature of 650.degree. C. on the hastelloy metallic substrate which is Ni-based alloy by means of laser physical vapor deposition(LPVD) method in which excimer laser is employed, deposite YBa.sub.2 Cu.sub.3 O.sub.7-x (hereinafter referred to Y-system superconductor) film, and obtain a high-temperature superconducting thin film of critical current density(Jc) of 7000 A/cm.sup.2 (77 K., 0T). Further, on pages 976 to 978 in "Applied Physics Letters, vol. 61, No. 8 (Aug. 24, 1992)", Ashok Kumar et al. report that titanium nitride(TiN) is employed as the intermediate buffer layer to form an oxide superconducting thin film where Y-system superconductor is formed on the hastelloy metallic substrate with the intermediate layer, whereby critical current density of around 9.0.times.10.sup.4 A/cm.sup.2 (77 K.,0T) is obtained. Here, the process for depositing the intermediate layer comprises the step of radiating KrF excimer laser to TiN target by the PVD method mentioned above where the metallic substrate temperature of 600.degree. C. and the pressure less than 10.sup.-6 Torr are employed.
On page 769 to 771 in "Applied Physics Letters, vol. 60, No. 6 (Feb. 10, 1992)", Iijima, an employee of K. K. Fujikura who is one of the applicants of this application, and others report that they make an oxide superconducting thin film which is formed with hastelloy metallic substrate/YSZ intermediate layer/Y-system superconductor, wherein critical current density(Jc) is 2.5.times.10.sup.5 A/cm.sup.2 (77 K.,0T) at maximum. The process for depositing an intermediate layer used herein is called ion-beam assisted deposition(IBAD) method, wherein it comprises sputtering YSZ target by Ar ion-beam at the pressure less than 3.0.times.10.sup.-4 Torr, and radiating Ar and O ion-beam (ion-beam bombardment) to a substrate during film deposition. At this time, the film deposition temperature reaches near 100.degree. C. by ion-beam radiation.
By the above process for depositing the oxide superconducting thin film on the substrate on which the intermediate buffer layer is formed, the oxide superconducting thin film with relatively high current-transport properties is obtained, however, there are disadvantages in that it takes a long time and it is impossible to manufacture long or large area products like a wire and a magnetic shield material at one step. On the other hand, it is desired to deposit a high-temperature superconducting thin film having higher quality and higher current-transport properties for use as wires, cables, tapes, magnetic shield, current leads and the like. Accordingly, it is required to improve the quality of an intermediate buffer layer on the metallic substrate, wherein the intermediate buffer layer becomes the base material for depositing the oxide superconducting thin film thereon.
Meanwhile, there is thermal plasma flash plasma evaporation method as one of methods for depositing an oxide film on a substrate. The thermal plasma flash plasma evaporation method is comprised of depositing an oxide film on the substrate with high-frequency plasma of a superhigh temperature. When this method is applied to the film deposition of an intermediate buffer layer and an oxide superconducting thin film, it can be expected that the film deposition with high rate on a and large area in comparison with another method of film deposition is performed. However, since the deposition by the high-frequency plasma which is suitable for a ceramic substrate which is stable at a high temperature requires superhigh-temperature plasma gas, there is a disadvantage in that a reaction product between plasma and a metallic substrate tends to be formed on the metallic substrate, when the metallic substrate is easier to react with plasma in comparison with the a ceramic substrate.